Chemotherapy drugs are medicines used to kill cancer cells and possibly prevent cancer from spreading. These drugs are also called anti-cancer drugs or chemotherapeutic agents. There are more than 80 anti-cancer drugs available, with many more being studied. Each type of anti-cancer drug works in a slightly different way. In general, they all kill cancer cells, or interfere with the ability of cancer cells to divide and grow, which can limit the size of cancerous tumors. In killing cancer cells, the use of chemotherapy also may prevent cancer from spreading (metastasizing) to other parts of the body, such as to the bone, brain, liver or lungs.

Anti-cancer drugs come in many different combinations, and specialists called oncologists who use them follow many different treatment schedules. Because of the many ways cancer cells grow, the use of combinations of chemotherapy drugs (rather than a single drug) have been shown to be more effective, as the combinations can result in more-effective elimination of the cancer cells. Each person's chemotherapy plan depends on the cancer being treated and how far the cancer has spread.

Chemotherapy is generally given by administering the drugs through a vein, as most people receive anti-cancer drugs through a process called intravenous infusion. A bag filled with the liquid drug is attached to a tube that is inserted into a vein. The drug slowly drips into the patient's body. Other people get their anti-cancer drugs from injections or in pill form.

Chemotherapy drugs reach almost all parts of the body. This is called systemic therapy, since the chemotherapy may eliminate the presence of microscopic cancer cells that have not yet become large enough for physicians to detect through the use of x-rays or other diagnostic testing. Administering the chemotherapy through the vein helps to kill cancer cells that have spread from the original site of the cancer. Because of the structure of the brain and the testes, often chemotherapy may not necessarily penetrate into these tissues. Frequently treatment programs may use additional methods to attempt to eliminate the cancer cells that may be present in these two areas, since the brain and the testes usually are exposed only to very low concentrations of chemotherapy drugs. Cancers in these areas may be treated differently.

Unfortunately, cancer chemotherapy agents are not specific for cancer cells. This means that anti-cancer drugs attack more than just cancer cells. Normal, healthy cells are destroyed as well, especially cells lining the mouth, digestive tract, and hair follicles and the blood cells within bone marrow. This is why many people receiving chemotherapy get mouth sores and upset stomachs, lose their hair, and feel weak. A common side effect of chemotherapy is increased susceptibility to infections because the chemotherapy knocks down the production of new blood cells in the bone marrow. When white cell counts get too low, the body loses the ability to fight bacteria, viruses and other germs. These infections can be very serious and often require hospitalization. The risk of infection lessens when the white blood counts recover.

The bone marrow also produces specialized cells that are required for blood clotting. Chemotherapy can also affect these cells, leading to an increased risk of bleeding. The cells involved are called platelets. As the effects of chemotherapy wear off on the bone marrow, the risk of bleeding also diminishes.

For some cancers, especially those that arise from the blood and bone marrow cells, such as leukemia and multiple myeloma, chemotherapy is the mainstay of treatment. For other cancers, especially those that are referred to as solid tumors, (e.g., breast, colon, lung and others arising from an organ) chemotherapy is one part of a larger strategy that also involves radiation and/or surgery. Chemotherapy can destroy tumors or slow the growth of the cancer. Chemotherapy also can relieve symptoms and improve the quality of life for people with advanced cancer that cannot be destroyed or slowed.

Each type of anti-cancer drug produces its own set of side effects, which may be more or less severe depending on your body's reaction to the drug. Always ask your doctor about the possible side effects of your anti-cancer treatment before chemotherapy begins.

Anti-cancer drugs can be given in a hospital, clinic, or doctor's office or even at home. Sometimes the treatment is as easy as swallowing a pill. Other times it requires an injection or a more complicated procedure in which the drugs are delivered slowly through intravenous infusion. People can receive chemotherapy daily, weekly or monthly. Sometimes there is a rest period between sessions. This allows the body to recover from side effects before the next wave of treatment begins.

Doctors use different tests to judge how well chemotherapy is working: physical exams, magnetic resonance imaging (MRI) and computed tomography (CT) scans, X-rays and blood tests. Because chemotherapy affects the production of red and white blood cells and platelets, doctors order frequent blood counts to evaluate the need for medicines to stimulate the bone marrow and/or transfusions. The blood tests also are used to make sure that liver and kidneys have not been injured by the chemotherapy.

Anti-cancer drugs can cause many side effects. Common ones include fatigue, nausea and vomiting, diarrhea, mouth sores, hair loss, rashes, and low levels of several types of blood cells. Blood cell problems may increase your risk of infections and bleeding. Your doctor has methods to decrease the severity of many of these side effects. Other side effects depend on the specific anti-cancer drugs used and include allergic reactions, numbness and tingling in the hands and feet, irritation of the veins injected with the drug, and bleeding from the bladder.

Because anti-cancer drugs can cause birth defects, particularly if used early in pregnancy, tell your doctor if you may be pregnant. Also, some chemotherapy drugs can cause infertility. Adults in their childbearing years should ask their doctors about the impact of chemotherapy on family planning.

Call your doctor if you have any of the following problems during chemotherapy:

Fever

Chills

Rash

Swelling of your hands, feet or parts of your face

Severe vomiting

Diarrhea

Blood in your urine or bowel movements

Any abnormal bleeding or bruising in the skin

Trouble breathing

Severe headaches

Any unexplained pain that is severe or lasts for long periods

If anti-cancer drugs were injected, call your doctor if you develop pain, swelling or redness at the injection site.

Depending on the type of chemotherapy, there may be other side effects to watch for. Your doctor will discuss them with you before treatment starts.

You may need some help adjusting your daily routine to deal with the side effects of chemotherapy. For example, if your anti-cancer treatment increases the effects of sunlight on your skin, you may need to change your schedule of outdoor activities or wear protective clothing and sun-blocking lotions. You may also need to stop taking certain medications, such as aspirin, cough medicine and sleeping pills, because they can interfere with some chemotherapy drugs. Your doctor can suggest ways to minimize the effects of chemotherapy.